A booby-trapped package exploded next to the office of the Greek minister in charge of the police force on Thursday, killing one of his aides, officials said.
No one immediately claimed responsibility for the blast, which occured on the seventh floor of the ministry and caused serious damage to the office of Civil Protection Minister Mihalis Chrysohoidis.
"It was a wrapped package that exploded in the aide's hands after he apparently picked it up and tried to open it," police spokesman Thanassis Kokkalakis told Reuters. "We heard a big bang, there was a lot of smoke and damage".
There was no warning and no reports of other injuries.
Since suffering its worst riots in decades in 2008, Greece has been rocked by a series of bomb attacks for which lefist militants have claimed responsibility. Earlier this year, police arrested six suspected members of the country's most violent militant group, Revolutionary Struggle.
When he took office in 2009, Chrysohoidis promised to crack down on militants. In a previous spell in the job in 2002, he dismantled November 17, Greece's most lethal guerrilla group.
The victim of Thursday's blast, George Vassilakis, was adjutant to the minister and the father to two children.
"I lost a valuable and dear colleague," an emotional Chrysohoidis told reporters outside the ministry. He was in the building at the time of the explosion at 8.15 p.m. (1715 GMT), but escaped injury.
In early May, three people including a pregnant woman were killed when people marching in an anti-austerity protest fire-bombed an Athens bank. In March, a 15-year old boy was killed and his mother and sister injured after a bomb exploded outside a building in the capital.
Debt-choked Greece is facing a deep economic crisis and last month won a 110 billion euro ($147.6 billion) bailout package from the European Union and the IMF in exchange for draconian austerity measures.
"In a time when our country and our people wage a daily battle to escape the crisis, cowardly murderers are striking a blow at our democracy," Prime Minister George Papandreou said late Thursday in a statement.
